WaterAnswer.com

Chloramines vs. Chlorine in Tap Water: Key Differences

About 30% of US community water systems now use chloramines instead of free chlorine. If your utility switched in the last 20 years, the water behaves differently at your tap than it used to. The disinfectant is still working, but your old filter may not be.

How Chloramine Forms and Why Utilities Use It

Chloramine isn’t a naturally occurring compound. Your utility creates it on purpose by adding ammonia to water that’s already been chlorinated. The result is monochloramine, the most common form used in drinking water treatment.

Utilities made the switch for a specific regulatory reason. When chlorine reacts with naturally occurring organic matter in source water, it forms trihalomethanes (THMs) and haloacetic acids (HAAs). Both are regulated as potential carcinogens. The EPA tightened its rules on these disinfection byproducts in the late 1990s with the Stage 1 Disinfectants and Disinfection Byproducts Rule. Chloramine produces far fewer of them.

Chloramine also has better staying power in distribution pipes. Free chlorine dissipates as water travels from the treatment plant to your tap. Chloramine holds its concentration longer, which means water at the far end of the distribution system still has disinfectant residual.

So the switch was a tradeoff. Utilities chose a disinfectant that creates fewer regulated byproducts and maintains better pipe residual. What they didn’t change is the basic goal: keep microbial contamination out of drinking water.

Four Ways Chloramine Behaves Differently from Chlorine

The differences matter for how you treat your water at home.

It doesn’t off-gas. Free chlorine is volatile. Leave a glass of chlorinated tap water on the counter for a few hours and the chlorine smell fades. Leave it overnight and most of the chlorine is gone. Chloramine doesn’t work that way. It’s chemically stable and stays in solution. Letting water sit in an open container doesn’t meaningfully reduce it.

It requires different filter media. Standard activated carbon removes free chlorine quickly through a chemical reduction reaction. Chloramine’s bond is more stable. Standard carbon works on it too slowly to be reliable at the flow rates most filters use. Catalytic carbon is the right media for chloramine.

It’s toxic to fish and dialysis patients. Both chlorine and chloramine are toxic to fish, but chloramine is more persistent in water and harder to remove from dialysis equipment. Dialysis centers must treat water specially when their supply uses chloramines. Fish tank owners can’t assume the standard dechlorinating drops they’ve always used will handle it.

It forms different byproducts. Chloramine reduces regulated THMs and HAAs but forms other byproducts including N-nitrosodimethylamine (NDMA) and iodoacids. These are less studied than THMs. Some have higher toxicity per unit than the regulated byproducts chloramine was meant to replace. The tradeoff isn’t that chloramine is cleaner. It’s that it creates a different set of concerns that are still being studied.

Why Your Filter Choice Changes

This is the most practical difference for most households.

A pitcher filter or faucet-mount filter with standard granular activated carbon (GAC) will work reasonably well on free chlorine. The same filter on a chloramine supply may show little to no reduction because standard carbon doesn’t break the chloramine bond fast enough at typical flow rates.

Catalytic carbon is different. It has a modified surface structure that reacts with chloramine more efficiently. The same contact time that does little with standard carbon will substantially reduce chloramine with catalytic carbon.

When you’re buying a filter for chloramine reduction, check the NSF certification. Look specifically for NSF/ANSI 42 certification that lists chloramine reduction. Some filters are NSF 42 certified only for chlorine reduction. The NSF certification database at nsf.org lets you look up any certified product and see exactly what it’s been tested for. Don’t rely on packaging language alone.

For drinking water, an under-sink catalytic carbon filter or a reverse osmosis system will address chloramine reliably. RO removes chloramine and gives you broader contaminant coverage at the same time.

The Pipe Corrosion Question

A 2007 study published in Environmental Health Perspectives examined Washington, D.C.’s experience when the city switched to chloramines in 2000. The study found that blood lead levels in children increased during that period. The proposed mechanism: chloramine is less effective than free chlorine at maintaining a protective mineral scale on lead pipes. Without that scale, lead leaches more readily into water.

This study has limitations. It was a single city with a high proportion of lead service lines. The researchers noted that the relationship between disinfectant type and lead leaching depends heavily on the specific chemistry of the water and the pipe material. Not every utility that uses chloramines will see the same effect.

The practical implication: if your home has lead service lines, lead solder, or brass fixtures installed before 1986, and your utility recently switched to chloramines, it’s worth testing your tap water for lead. The CDC’s recommendation hasn’t changed, but the context has.

Read more about the lead connection on our lead contamination page.

How to Find Out What Your Utility Uses

Your utility is required to tell you. The easiest source is your Consumer Confidence Report (CCR). Every public water system serving 25 or more people must publish one annually. It lists the disinfectant used and any measured disinfection byproduct levels.

If you don’t have the CCR handy, call your utility’s customer service line and ask directly: “Do you use free chlorine or chloramines for disinfection?” It’s a routine question they field regularly.

You can also look up your utility in the EPA’s Safe Drinking Water Information System (SDWIS) database, though the CCR is easier to read.

Our guide to reading your Consumer Confidence Report explains where to find the disinfectant information and what else to look for.

If you confirm your utility uses chloramines, the next step is checking whether your current filter is certified for chloramine reduction, not just chlorine. That one distinction determines whether it’s doing anything useful.

See our chloramines hub page for a full overview, or jump to how to remove chloramines from tap water for filter recommendations.

Sources

Frequently Asked Questions

Does chloramine taste different from chlorine in tap water?
Many people find chloramine has a different taste from free chlorine. Some describe it as a slight bitterness or chemical taste distinct from the pool-like taste of high chlorine. Both come from disinfectants. If your taste concern changed when your utility switched disinfectants, that's likely the cause. Catalytic carbon filters address both, though the filter media required differs.
Can I use standard dechlorinating drops for chloramine when filling a fish tank?
No. Most standard dechlorination products neutralize free chlorine but not chloramine. Chloramine is more stable and requires a different chemical to neutralize. If your utility uses chloramines and you have a fish tank, use a dechlorinator labeled specifically for chloramine removal. The product will say "neutralizes chloramine" or "removes chloramine." Don't assume a product handles both because it handles one.
Does letting water sit overnight remove chloramine?
Not effectively. Free chlorine will off-gas significantly if you leave water uncovered for several hours. Chloramine is much more stable and doesn't off-gas meaningfully at room temperature. If your utility uses chloramines, letting water sit overnight won't reduce it to a level that makes a meaningful difference. You need a filter specifically effective against chloramine.
Is chloramine safer than chlorine?
Both are regulated disinfectants with EPA limits. At typical treatment concentrations, neither poses significant direct risk to most people. The comparison isn't really about which is safer. It's about which creates fewer harmful byproducts. Chloramine creates fewer regulated disinfection byproducts (THMs, HAAs) but forms different unregulated byproducts that are still under study. The tradeoff is about byproduct profiles, not disinfectant safety.
Why is chloramine harder to filter out?
Free chlorine reacts readily with activated carbon. The reaction breaks down chlorine quickly, which is why standard carbon filters work on chlorine. Chloramine forms different chemical bonds that are more stable. Standard activated carbon works much more slowly on chloramine, often not fully reducing it within a normal filter contact time. Catalytic carbon has a different surface structure that breaks the chloramine bond more efficiently.